Chronic low back pain (CLBP) is the most common pain condition among returning Veterans and is associated with high levels of opioid analgesic prescribing in VA clinics. Although prescription opioids are effective for acute pain, evidence does not support their long-term effectiveness and they are associated with increased risk of addiction, diversion, overdose and death. Substantial gaps in the non-pharmacologic treatment of chronic pain exist and there is little scientific evidence available to guide the provision of cre. Cognitive behavioral therapy (CBT) is the most widely used non-pharmacologic treatment for pain; however, its effects on pain are modest when used in isolation. Enhancing the effectiveness and durability of CBT is critical to providing a viable non-pharmacologic treatment option to the millions of Veterans suffering from chronic pain. Transcranial Direct Current Stimulation (tDCS) is a novel, minimally-invasive brain stimulation technique that demonstrates analgesic effects when applied over the dorsolateral prefrontal cortex (DLPFC). Accumulating data from our group and others suggest that tDCS may augment the treatment effects of CBT for chronic pain. However, no studies to date have directly investigated potential synergistic effects of combining these therapies. The proposed study directly addresses this gap in the literature by testing the feasibility and preliminary efficacy of tDCS in combination with CBT to reduce pain and opioid use severity among U.S. military Veterans who have served in Operation Enduring Freedom, Operation Iraqi Freedom or Operation New Dawn (OEF/OIF/OND) and have current CLBP and co-morbid prescription opioid use disorders. tDCS may prime and modulate prefrontal circuitry resulting in enhanced capacity to tolerate and down-regulate the emotional component of pain experience, while CBT can teach the skills necessary to maintain these gains, thus resulting in a synergistic effect. The primary objective of the proposed Stage II study is to evaluate the effects of CBT in combination with tDCS in (1) improving pain and functionality, (2) reducing severity of opioid use disorders, and (3) reducing impairment in associated mental health areas (e.g., other substance and prescription drug use, depression, anxiety, PTSD, sleep). To accomplish this we are: using a manualized, evidence-based CBT intervention; employing a randomized between-groups, double-blind experimental design (CBT + tDCS vs. CBT + sham tDCS); and examining standardized, repeated dependent measures of change at 5 time points (pre- and post-treatment; 1, 3 and 6 month follow-up). This project is directly responsive to the mission of the National Institute on Drug Abuse (NIDA) and the National Center for Complementary and Alternative Medicine (NCCAM) in that it seeks to accelerate clinical trial research on non-pharmacologic approaches to manage pain and comorbid conditions. The findings of this study will provide empirical evidence to inform polices and programs to better serve the needs of U.S. military personnel and Veterans.